Nylon is a series of polymers with a general formula —[(CH2)n—CONH]— or —[(CH2)n—CONH—(CH2)m—NHCO]—, typically named with the length of the methylene units separating the amide functions. Some such examples are nylon 6, nylon 6-6, nylon 7, nylon 8, nylon 9, nylon 11, nylon 12, and nylon 13. Certain nylons, such as nylons 11 and 12, possess excellent chemical resistance, thermal resistance, cold impact resistance, flexibility, and durability. There are many industrial applications of these nylons, including automotive applications, sports applications, medical applications, high-performance cables, electronics, electrical materials, and lenses for glasses. Currently, about 100,000 metric tons of nylon 11 and nylon 12 are produced annually. The use of these nylons in the automotive/transportation industry is increasing at an annual rate of 33.7%, extrapolated to 250,000 metric tons by 2016. Similarly, their use in photovoltaic panels is expected to increase at an annual rate of 36.1% through 2016, and in other general applications is predicted to increase at a rate of 25.3% annually through 2016. Nylon 13 has analogous characteristics to nylon 12 and may be used in similar applications as nylon 12.
Nylon 11, 12, and 13 can be produced from amino acids or their derivatives such as esters or lactams. Currently, the main supply source of C12 amino acid (in lactam form) is produced from petroleum-derived butadiene in a six-step process. While the carbon backbone can be obtained from petrochemical sources by chemical synthesis, there is an increasing interest in the use of renewable resources for the production of this and similar amino acids (and their derivatives), due to growing environmental and sustainability concerns.
Nylon precursor synthesis approaches that use natural fatty acids and esters from plant- or algae-derived biomass as the starting materials are especially attractive methods for producing nylon precursors. Among the natural fatty acids, oleic acid is the predominant component of lipids in most vegetable oils (e.g. soy oil) and algae. While pathways for producing nylon 11 from oleic acid are known, the methods currently used are unsuitable for producing nylon 12 or nylon 13 from the abundantly-available oleic acid. This, in large part, is because of the formation of undesirable isomers produced in the key step, resulting in low overall yields when existing art is applied to produce C12 and C13 amino acids from oleic acid. Accordingly, the methods currently used require more exotic fatty acids to produce nylons 12 and 13. For example, recinoleic acid from castor oil is used to produce C11 and C12 amino acids and esters, while erucic or lesquerolic acid is used to produce a C13 lactam (cyclic amide of C13 amino acid). In one method, erucic acid is first oxidized to produce brassylic acid (a diacid with 13 carbons), which is subsequently converted, over several steps, into a C13 lactam. The lactam can be polymerized to nylon 13. In another method, caster oil is converted to 11-aminoundencanoic acid (C11 amino acid) by a process that begins with base-catalyzed methanolysis of castor oil, which generates methyl recinoleate. The recinoleate is then subjected to a retro-prins reaction to obtain heptanaldehyde and methyl undecyleate. After separation, the latter is hydrolyzed to acid, followed by conversion to an ω-bromo acid by hydrobromination. Finally, the bromine is replaced by an amine over 5-6 steps to produce 11-aminoundecanoic acid.
In a similar approach to produce 11-aminoundecanoic acid from oleic acid, oleic acid or ester is first converted to α-ω-diacid or diester by either homometathesis or enzymatic conversion. After separation and recovery of the diacid or diester from the reaction mixture, they are subjected to oxidative cleavage to produce α-ω-formylacids or esters. The aldehyde is converted to an amine by reductive amination in the final step. The process of generating fatty amino acids of other chain lengths (C9 to C15) is possible using a similar method, starting from other natural fatty acids or their derivatives.
Another approach to produce 11-aminoundecanoic acid and 12-aminododecanoic acid from components of castor oil—oleic acid and recinoleic acid—involves subjecting oleic acid or ester to a cross metathesis reaction with acrylonitrile to produce 10-cyano-9-decenoic acid or ester, followed by reduction using high-pressure hydrogenation to remove unsaturation. (PRIOR ART FIG. 1A.) 12-aminododecanoic acid is also prepared in analogous fashion starting from 10-undecenoic acid prepared from pyrolysis of recinoleic acid. (PRIOR ART FIG. 1A.) It has been reported that α-ω-diacids or diesters synthesized by homometathesis or fermentation, or acids or esters with a terminal olefin prepared from ethylenolysis, can also be used as the starting material in lieu of oleic acid.
Another method starts with either 9-decenoic or 10-undecenoic acids or esters (or other ω-terminal fatty acids with various chain lengths) that are subjected to cross-metathesis with either 2-pentenenitrile or 3-pentenenitrile or unsaturated amine, resulting in unsaturated nitrile or amino acids or their esters. The produced unsaturated nitriles and esters are hydrogenated using 5 mol % Raney nickel-cobalt under a high-pressure hydrogen atmosphere. This method produces amino acids with various chain lengths. A similar method can be used for hydrocyanation of 10-decenoic acid and subsequent hydrogenation for C12 amino acid production, as well as polymerization of linear amino acids to polymers. However, the cross-metathesis yields from this method are generally low (between 13-30%), particularly when 3-pentenenitrile is used to produce nylon 12 amino acid.
There is a need for additional and improved renewable methods of producing nylons, and their precursors, that are simpler or cheaper or that involve milder reaction conditions.